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PubMed1995

The missing temporal crescent.

PURPOSE: We studied clinically the representation of the monocular temporal crescent in the human visual cortex and noted the importance of using the perimetric techniques best suited to detect this visual field defect and to study patients in whom the temporal crescent is missing. METHODS: Goldmann perimetry and high-resolution magnetic resonance imaging were performed in two patients with vascular lesions located in the anterior striate cortex. RESULTS: A monocular visual field defect, the missing temporal crescent, was found on the side contralateral to the lesion. CONCLUSIONS: The perimetric-magnetic resonance imaging correlation is in exquisite agreement with recent information about the representation of the visual field in the human primary visual cortex. Reports of this specific perimetric finding are rare, in part because of underdetection with currently used perimetric techniques that concentrate on the central 30 degrees of the visual field.

Adult↗
PubMed1999

[Visual hallucinations and illusions, symptoms frequently misdiagnosed by the practitioner].

INTRODUCTION: Visual hallucinations or illusions are not a rare symptom. However, they are often unrecognized. Unawareness of the meaning of these symptoms often mislead both the patient and his physician. PURPOSE: To define and describe the types of visual illusions and hallucinations which can be commonly encountered in neuro-ophthalmological practice. METHODS: Overview article. RESULTS: Hallucinations are a perception not based on sensory input, whereas illusions are a misinterpretation of a correct sensory input. Both phenomenon can be due to medication or drug, or to an altered mental status. Visual hallucinations can be formed (objects, people) or unformed (light, geometric figures). They can be generated either by a lesion on the antechiasmatic pathway, by a seizure phenomenon, by a migrainous phenomenon, or by a release phenomenon secondary to visual differentiation. Investigations will be directed towards a retinopathy, an optic neuropathy, a chiasmal or retrochiasmal lesion, or a bilateral antechiasmal lesion (Charles Bonnet syndrome). Visual illusions include meta-morphopsias, micro- macropsias, polyopia, palinopsia (visual perseveration), achromatopsia, Pulfrich phenomenon, or subjective vertical deviation. Illusions can be due to lesions of the retina, the optic nerve, the visual cortex (primary or associative), or the graviceptive pathways. CONCLUSIONS: As most patients do not spontaneously mention their symptoms, history taking is essential. The first step is to rule out medication or an altered mental status as the possible cause of these symptoms. Then, careful visual function examination should provide a good insight in the location of the lesion.

Diagnosis, Differential↗
PubMed1993

Distribution of seven major neurotransmitter receptors in the striate cortex of the New World monkey Callithrix jacchus.

The distribution of seven different binding sites for the transmitters L-glutamate (L-glutamate binding sites and N-methyl-D-aspartate receptor), GABA (GABAA receptor), noradrenaline (alpha 1 receptor), acetylcholine (muscarinic M1 and M2 receptors) and serotonin (5-hydroxytryptamine1 receptor) are analysed in the primary visual cortex (area 17) of the common marmoset, Callithrix jacchus, using quantitative autoradiography. All binding sites show a well-defined laminar pattern, which changes sharply at the cytoarchitectonic border to area 18. The quantitative data show that the distribution of different receptors is relatively invariant across the cortical layers. Almost all receptors show a maximum in supragranular layers, low densities in layers IVA/IVB and a second maximum in layer IVC. Statistical analysis of these similarities in laminar distribution patterns of different receptors (co-distribution) reveals, as in other brain regions and species, that L-glutamate binding sites are co-distributed with N-methyl-D-aspartate, GABAA, and muscarinic M1 and M2 receptors. This may reflect the structural basis of a possible interaction between these receptors and their respective transmitters on the level of single cortical layers. Further co-distributions are found between N-methyl-D-aspartate, GABAA and M1, as well as between alpha 1 and M1 and finally between M1 and M2 receptors. Since not all receptors are co-distributed, the similarities in laminar patterns reveal specific aspects of the neurochemical organization of the cortex when receptors of different transmitter systems are analysed in the same brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1999

Co-expression of TrkB and the N-methyl-D-aspartate receptor subunits NR1-C1, NR2A and NR2B in the rat visual cortex.

In the visual cortex, brain-derived neurotrophic factor expression is modulated through glutamate receptors, including the N-methyl-D-aspartate glutamate receptor. It has been proposed that the N-methyl-D-aspartate glutamate receptor subunit composition itself might be regulated by brain-derived neurotrophic factor. Here, we investigated the co-expression of the neurotrophin-4/brain-derived neurotrophic factor receptor TrkB with the N-methyl-D-aspartate glutamate receptor subunits NR1-C1, NR2A and NR2B, on postnatal days 10 and 22 and in the adult rat primary visual cortex. At both postnatal days 10 and 22, TrkB is co-expressed in all cortical layers with the studied N-methyl-D-aspartate glutamate receptor subunits. In the adult, in layers IV-V, co-expression is restricted to a subpopulation of neurons, while in layers II-III, VI nearly all neurons co-express TrkB with NR1-C1, NR2A and NR2B. We conclude that in layers IV-V, the co-expression of TrkB with subunits NR2B and NR2A is developmentally regulated.

Aging↗
PubMed1991

Energy filters, motion uncertainty, and motion sensitive cells in the visual cortex: a mathematical analysis.

Energy filters are tuned to space-time frequency orientations. In order to compute velocity it is necessary to use a collection of filters, each tuned to a different space-time frequency. Here we analyze, in a probabilistic framework, the properties of the motion uncertainty. Its lower bound, which can be explicitly computed through the Cramér-Rao inequality, will have different values depending on the filter parameters. We show for the Gabor filter that, in order to minimize the motion uncertainty, the spatial and temporal filter sizes cannot be arbitrarily chosen; they are only allowed to vary over a limited range of values such that the temporal filter bandwidth is larger than the spatial bandwidth. This property is shared by motion sensitive cells in the primary visual cortex of the cat, which are known to be direction selective and are tuned to space-time frequency orientations. We conjecture that these cells have larger temporal bandwidth relative to their spatial bandwidth because they compute velocity with maximum efficiency, that is, with a minimum motion uncertainty.

Animals↗
PubMed2003

Experience-dependent regulation of the zincergic innervation of visual cortex in adult monkeys.

Zinc is packaged in, and released from, a subset of glutamatergic synapses in the mammalian telencephalon where it has been shown to act as a potent neuromodulator. In order to establish the functional role for zincergic neurons in visual cortical function and plasticity we have compared the topographic distribution of zincergic terminals in the primary visual cortex (V1) of normal adult vervet monkeys (Cercopithicus aethiops) to that in monkeys monocularly deprived of visual input for short (24 h) or long (3 months) survival times. In normal animals, staining levels for zinc were highest in layers 1-3, 4b, 5 and 6 and lowest in layers 4a and 4c. The laminar and tangential patterns of zinc staining were complementary to staining patterns demonstrated using cytochrome oxidase (CO) histochemistry. Following 3 months of monocular deprivation by enucleation, levels of zinc staining in layers 3, 4calpha and 6a were heterogeneously reduced, clearly revealing the ocular dominance pattern in V1. When compared with the pattern of CO staining, levels of both CO and zinc were reduced in cortical territory innervated by the enucleated eye. Zinc histochemistry also revealed the ocular dominance pattern after only 24 h of monocular impulse blockade induced by enucleation or intravitreal tetrodotoxin infusion. However, by either means of deprivation for 24 h, levels of zinc were increased in deprived-eye stripes relative to nondeprived-eye stripes. These results indicate that zincergic terminals demarcate distinct compartments in the primate visual cortex. Furthermore, levels of synaptic zinc are rapidly and dynamically regulated, suggesting that zinc and/or zincergic neurons participate in mediating activity-dependent changes in the organization of the adult neocortex.

Animals↗
PubMed1985

Noradrenaline and functional plasticity in kitten visual cortex: a re-examination.

A quantitative re-examination was made of the influence of noradrenergic depletion on the epigenesis of kitten visual cortex. Two methods were used to deplete noradrenaline at the cortical level: stereotaxically controlled injection of 6-hydroxydopamine (6-OHDA) in the coeruleus complex, from which the noradrenergic input to visual cortex arises; intraventricular injection of 6-OHDA. The latter chemical lesion also depleted dopamine levels in the brain. Lesion of the noradrenergic or catecholaminergic systems was performed neonatally or at an age of 3-4 weeks in kittens submitted to five different rearing procedures: normal rearing, dark rearing, monocular rearing, monocular exposure following dark rearing and monocular deprivation following normal rearing. Forty-two kittens between 3 and 12 weeks of age were used for this biochemical and electrophysiological study. Noradrenaline and dopamine levels were measured by a radioenzymatic method in the primary visual cortex of twenty-six kittens. A total of 1263 cells were recorded in area 17 of twenty-six kittens. Combined biochemical and electrophysiological data were obtained in ten 6-OHDA-lesioned kittens. Whatever the mode of chemical lesion used, cortical noradrenergic depletion failed to block either maturation or vision-dependent processes which are known to affect orientation selectivity and/or ocular dominance during the critical period. However, in some cases, the amplitude of the epigenetic functional modifications was slightly reduced in 6-OHDA-treated kittens. The cortical effects of monocular deprivation starting from the age of 5 weeks were studied quantitatively both in lesioned and intact kittens. Disappearance of noradrenaline in area 17 did not prevent the loss of binocularity in cortical cells. However, even when monocular occlusion had been maintained for 2 or 3 weeks in 6-OHDA-treated kittens, ocular dominance shifts were limited to a stage equivalent to that observed in the intact kitten after 5-8 days of monocular occlusion. The amplitude of this partial protective effect was found to be unrelated either to the delay following the chemical lesion, or to the level of noradrenaline remaining in lesioned kitten cortex. Although a putative gating role of noradrenaline cannot be excluded in the development of the intact animal, this report shows that its presence is not required for functional plasticity to occur in kitten area 17.

Animals↗
PubMedDate not supplied

Oscillopsia associated with dysfunction of visual cortex.

PURPOSE: To investigate the cause of oscillopsia without nystagmus or vestibular dysfunction in a 31-year-old man with no past history of serious illness. METHODS: The changes in the regional cerebral blood flow elicited by visual stimuli were studied by positron emission tomography (PET) in the patient and were compared with changes in normal subjects. The primary visual cortex (PVC) and area V5 were defined on Talairach coordinates, as shown in previous PET studies, and were confirmed with their activation patterns in our subjects. RESULTS: Flicker stimulation (8 Hz) and a stationary random dot pattern activated area V5 in the patient, but not in the six normal controls. A moving random dot pattern activated both the PVC and the extra-striate cortex in both the patient and the controls. CONCLUSIONS: Oscillopsia in this case is associated with dysfunction of the visual cortices and may be caused by it.

Adult↗
PubMed2001

Magnetoencephalographic fields from patients with spontaneous and induced migraine aura.

We investigate and characterize the magnetoencephalographic waveforms from patients during spontaneous and visually induced migraine aura. Direct current neuromagnetic fields were measured during spontaneous onset of migraine auras in 4 migraine patients, and compared with recordings from 8 migraine-with-aura patients and 6 normal controls during visual stimulation of the occipital cortex. Complex direct current magnetoencephalographic shifts, similar in waveform, were observed in spontaneous and visually induced migraine patients, but not in controls. Two-dimensional inverse imaging showed multiple cortical areas activated in spontaneous and visually induced migraine aura patients. In normal subjects, activation was only observed in the primary visual cortex. Results support a spreading, depression-like neuroelectric event occurring during migraine aura that can arise spontaneously or be visually triggered in widespread regions of hyperexcitable occipital cortex.

Adult↗
PubMed2004

Oligodendrocytes, their progenitors and other neuroglial cells in the aging primate cerebral cortex.

In a previous study it was found that with age there is an increase in the frequency of paranodal profiles of myelinated nerve fibers in the cerebral cortex of monkeys. This indicates that there is an increase in the number of internodal myelin segments, and raises the question of whether additional oligodendrocytes are necessary to generate the increased numbers of internodal myelin segments. The present study shows that in layer 4C beta of monkey primary visual cortex there is an age-related increase in the number of oligodendrocytes. When young (4-10 years of age) and old (25-35 years of age) monkeys are compared, the increase is found to be approximately 50%, and it begins in middle age (12-19 years old). It is also shown that although there is no increase in the population of astrocytes in layer 4C beta with age, there appears to be a slight increase in the frequency of microglial cells. As their numbers increase, oligodendrocytes in pairs, rows and groups become more common, which suggests that additional oligodendrocytes are being generated by cell division. Since there is little evidence that mature oligodendrocytes can divide, it is probable that the new oligodendrocytes are generated from progenitor cells which, as many studies have shown, can be labeled by antibodies to NG2, a chondroitin sulfate proteoglycan. By comparing the appearance of these NG2-labeled cells with cells encountered in thin sections of normally prepared tissue, it is shown that the NG2-positive cells have the features of neuroglial cells that were previously described as beta astrocytes.

Aging↗
PubMed2005

Neural mechanisms of attentional modulation of perceptual grouping by collinearity.

Psychophysical research showed that detection of an oriented visual target is facilitated when the target is grouped with collinear visual flankers. However, this collinear grouping effect is evident only when the flankers are attended. This study examined neural mechanisms underlying the interaction between attention and grouping by collinearity. Event-related potentials were recorded from study participants who judged whether oriented Gabor patches (i.e. visual elements consisting of a sinusoidal contrast modulation convolved with a Gaussian function) along the cued orientation were collinear or orthogonal. Event-related potentials showed an enhanced negativity over the posterior occipital cortex at 48-72 ms when collinear patches were congruent rather than incongruent with the cued orientation. A negative shift between 260 and 380 ms was observed over the occipital-parietal areas in the congruent rather than incongruent conditions. The long-latency effect, however, was evident only when the collinear patches were allocated along 45 degrees . The event-related potential results suggest that the interaction between attention and collinear grouping may take place as early as in the primary visual cortex and is independent of global orientations of perceptual groups.

Adolescent↗
PubMed2000

Texture segregation in the human visual cortex: A functional MRI study.

The segregation of visual scenes based on contour information is a fundamental process of early vision. Contours can be defined by simple cues, such as luminance, as well as by more complex cues, such as texture. Single-cell recording studies in monkeys suggest that the neural processing of complex contours starts as early as primary visual cortex. Additionally, lesion studies in monkeys indicate an important contribution of higher order areas to these processes. Using functional MRI, we have investigated the level at which neural correlates of texture segregation can be found in the human visual cortex. Activity evoked by line textures, with and without texture-defined boundaries, was compared in five healthy subjects. Areas V1, V2/VP, V4, TEO, and V3A were activated by both kinds of line textures as compared with blank presentations. Textures with boundaries forming a checkerboard pattern, relative to uniform textures, evoked significantly more activity in areas V4, TEO, less reliably in V3A, but not in V1 or V2/VP. These results provide evidence that higher order areas with large receptive fields play an important role in the segregation of visual scenes based on texture-defined boundaries.

Adult↗
PubMed2001

Altered expression of alternatively spliced isoforms of the mRNA NMDAR1 receptor in the visual cortex of strabismic cats.

PURPOSE: Although much has been written about the role of the NMDA receptor's role in experience dependent visual plasticity, the function of the NMDAR1 receptor subunit in the post-plasticity stage of development is still not well understood. However, in the well studied model of strabismic amblyopia where binocularity is reduced, but where most primary visual cortex neurons can be driven by one or other eye, the density of expression of NMDAR1 receptor protein is significantly reduced, compared to normals. This study aims to identify which of eight isoforms of the spliced heterogeneous variants of the NMDAR1 mRNA receptor gene are associated with this decrease in expression as a means of elucidating possible function. METHODS: A series of digoxygenin-labelled oligonucleotide probes based on the human gene sequence have been used for in situ hybridization (ISH) of sections from the striate cortex of four adult cats. The probes were used to uniquely detect the expression of alternatively spliced mRNA variants in 66,487 cells from sections from the area centralis projection of two normal cats and two cats made esotropic as kittens by tenotomy at two weeks of age. RESULTS: As expected, total NMDAR1 mRNA isoform expression was significantly lower in the striate cortex of strabismic compared to normal cats. The proportion of cortical cells expressing the R1-a, R1-b, and R1-1 isoforms in strabismic animals was decreased while the proportion expressing R1-3 was increased, especially in layers V and VI. No significant difference in expression of the R1-2 and R1-4 isoforms was seen comparing strabismic and normal cats. CONCLUSIONS: These results confirm our previous findings and suggest that transcriptional inhibition of specific isoforms of NMDAR1 mRNA may underlie the change in receptor expression. This preferential reduction in the proportion of neurons bearing particular NMDAR1 isoforms, i.e. isoforms R1-a and b, and R1-1 with partial compensation through the expression of the R1-3 isoform, is more likely related to lowered proportion of binocularly activated neurons in the strabismic cat than to changes in eye dominance or the presence of amblyopia in one eye.

Alternative Splicing↗
PubMed1997

Cortical dynamics.

Our ability to interpret visual scenes involves assembling the components of objects into a unified percept and segregating them from background, storing information about earlier visual experiences and testing our interpretations of the visual world against incoming sensory input. The influences of context, experience and expectation are reflected in the response properties of cells at early stages in the visual pathway. The responses of cells in primary visual cortex depend not only on the attributes of features lying within the classical receptive field but also on the global characteristics of the contours and surfaces within which these features are embedded. The substrate for lateral interactions includes a plexus of long-range horizontal connections within each cortical area that links columns of similar orientation specificity and cells with widely separated receptive fields. The horizontal connections also play a role in the plasticity of receptive field structure and of cortical functional architecture, induced over long time scales by retinal lesions and over short time scales by patterned visual stimulation. The long-term changes are associated with synaptogenesis; and the short-term changes with an increase in synaptic effectiveness. The dynamics of cortical function persist throughout adulthood and are general to all cortical areas, including primary sensory cortices.

Animals↗
PubMed1989

The development of N-methyl-D-aspartate receptors in cat visual cortex.

During a critical period of early postnatal development, the visual cortex of kittens is susceptible to experience-dependent modifications of neuronal response properties. Recently, the activation of N-methyl-D-aspartate (NMDA) receptors has been identified as an indispensable prerequisite for the induction of such modifications. We therefore investigated developmental changes in the density and distribution of NMDA receptors and questioned whether these showed a relation to the time course of the critical period. We determined the proportion of [3H]glutamate binding sites that were displaced by the NMDA receptor antagonist 2-amino-5-phosphonovalerate (APV) on 10-microns-thick cryostat sections of the primary visual cortex. The overall density of APV-sensitive [3H]glutamate binding sites increased dramatically between the second and the fourth week and stayed at this level throughout the critical period. Towards the end of the critical period, these binding sites decreased and finally reached adult values that were slightly above those of 2-week-old kittens. APV-sensitive binding sites were present in all cortical layers of the age groups investigated. While the general pattern of developmental changes was similar in all layers, slight differences existed in the time course. These observations are compatible with the notion that NMDA receptor activation is required for the expression of use-dependent change of response properties in the kitten visual cortex. Furthermore, they suggest as a possible reason for the decline of malleability towards the end of the critical period the reduction of NMDA receptors.

2-Amino-5-phosphonovalerate↗
PubMed1996

The processing and encoding of information in the visual cortex.

Our knowledge of the response properties of visual cortical neurons has increased steadily since the original studies of Hubel and Wiesel in the 1960s. By comparison, an understanding of the neural mechanisms responsible for these properties has proved more elusive. Models for the mechanisms involved in even the most basic responses, such as the orientation tuning of simple cells in the primary visual cortex of the cat, remain controversial. Recent studies, however, are providing further support for a simple model (first suggested by Hubel and Wiesel), in which it is hypothesized that the response properties of simple cells in layer 4 of the cortex are dominated by the convergence of highly specific thalamic inputs.

Animals↗
PubMed1991

A correlation between gene transcriptional activity and cerebral glucose metabolism in Alzheimer's disease-affected neocortex: cause or effect?

Our laboratory has measured mRNA pool sizes in neocortex afflicted with Alzheimer's disease (AD). We have observed a repression of gene expression in the temporal and parietal regions compared to age-matched control neocortex. These changes in messenger RNA pool size closely parallel the observed alterations in local cerebral metabolic rates for glucose (LCMR-g), as detected by positron emission tomography (PET). For example, deficits in both gene transcription and glucose metabolism appear to be the greatest in AD-affected superior temporal neocortex (Brodmann area 22) but are less apparent in the primary visual cortex (Brodmann area 17) or in the cerebellum. The unresolved question is whether changes in gene expression are the cause or effect of altered glucose metabolism. However, the non-random reductions in the pool size for certain neocortical mRNAs argue in favour of altered gene expression as the primary event.

Alzheimer Disease↗
PubMed1996

A proposed reorganization of the cortical input-output system.

This paper proposes a new concept for interpretation of the cerebral cortex. In this schema, the cortex is an 'imaging system' which plays an integral part in the 'functional circuit' of the living body. This functional circuit is made up of five components: the 'imaging system' of the cortex, the 'image forming system' of the basal ganglia, thalamus and cerebellum, the 'image-acting system' of the brainstem and spinal cord, the 'sensory system' of the sense organs and the 'external words.' An image constructed in the cortex yields a purposeful movement by way of its outputs through the image-acting system. The image to drive the purposeful movement is formed and accumulated in the cortex by trial and error under the control of the image-forming system. In the proposed organization outlined here, the cortex can be divided into two components, both of which have their own input and output for forming and realizing the image. One is comprised of specific areas for analyzing proper sensations from the sense organs through a specific area of the thalamus (e.g., retinal to lateral geniculate to primary visual cortex). The other system is composed of non-specific areas analyzing more diffuse input from various sensory organs through non-specific areas of the thalamus. These two systems work in concert to form fundamental and detailed images for purposeful movements through tight intercortical connections. Whereas the outputs from non-specific areas yield common behaviors regardless of sensory modality, outputs from the specific areas controls movements related to a specific sensation. Thus, it is proposed that these two systems work cooperatively: the former constructs the image and causes the initial movements, and the latter controls the movements to realize the image from the changing information of transient conditions. This model differs from other models of cortical organization which segregate cortex on the basis of sensory-related input regions and motor-related output regions. Existing data is consistent with the proposed organizational scheme. Although it may be difficult to prove specific aspects of this new model. I believe that the hypotheses contained within it will serve as an important foundation for driving future research.

Afferent Pathways↗